1. Field of the Invention
The present invention relates to a thin film deposition apparatus used in a process of producing semiconductor devices and, more particularly, to an apparatus for deposition of thin films on a plurality of wafers through an atomic-epitaxial process within a reaction chamber, the apparatus being added with a plurality of units, such as a gas supply unit, a wafer heating unit and a gas discharging unit, thus improving productivity while producing semiconductor devices.
2. Description of the Prior Art
As well known to those skilled in the art, a conventional process of producing semiconductor devices comprises a wafer formation step, an epitaxy step, a thin film deposition step, a diffusion/ion-implantation step, a photolithography step and an etching step. That is, in order to produce desired semiconductor devices, a wafer is primarily formed from a polycrystalline silicon ingot made of a siliceous material, such as sand. A single crystalline film is formed on the wafer through an epytaxy step. Thereafter, a variety of thin films are formed on the wafer in accordance with desired use of resulting semiconductor devices prior to performing a diffusion/ion-implantation step. After the diffusion/ion-implantation step, the wafer is cut into a plurality of semiconductor chips. The chips are, thereafter, packaged by a plastic packaging material, thus forming desired semiconductor devices.
In the process of producing semiconductor devices, at least one film is formed on the wafer at every step. Such films, formed on the wafer during the process of producing semiconductor devices, are generally classified into four films: an oxide film (SiO.sub.2) typically used as a gate oxide film or a field oxide film, a nitride film (Si.sub.3 N.sub.4) typically used as an insulation film between conductive layers, a mask during a diffusion/ion-implantation step or a device protection film, a polycrystalline silicon layer typically used as a gate electrode in place of a metal film, and a metal film used as a conductive film connecting the devices together or connected to external terminals. Of course, it should be understood that the above-mentioned classification of the films into four types is not intended to limit the classification of such films.
In the prior art, a CVD (chemical vapor deposition) process has been-preferably used for forming an oxide film and a nitride film on a wafer. In such a CVD process, a plurality of wafers are positioned within a reaction chamber and a reaction gases are applied to the reaction surfaces of the wafers. The gases are thus vapor-deposited on the reaction surfaces of the wafers and form desired thin films on the reaction surfaces of the wafers. Such a CVD process is preferably used for accomplishing a deposition of thin films on wafers. Conventional CVD processes are classified into several types: an atmospheric CVD process, a reduced pressure CVD process, a plasma CVD process and an energy step-up CVD process. Regardless of the types of CVD processes, it is necessary to control the CVD processes so as to form a film having less impurities and a constant thickness on a target wafer.
A desired polycrystalline silicon film is formed on a wafer by thermally decomposing silane (SiH.sub.4) and vapor-depositing Si on the wafer within a reaction chamber. On the other hand, a desired metal film is formed on a wafer through a sputtering process or a CVD process. When such a CVD process is used for vapor deposition of such a metal film on a wafer, it is possible to accomplish high quality step coverage and a constant thickness of the resulting metal film and to form desired metal films on the reaction surfaces of a plurality of wafers at the same time.
The thin film deposition process is a very important process. In addition, the thin film deposition process is not performed only once during a process of producing semiconductor devices, but is repeatedly and necessarily performed at every step. Therefore, the thin film deposition technique has been actively studied to accomplish desired high quality film characteristics. As a result of such an active study, an apparatus, designed to deposit desired thin films on target wafers by positioning the wafers within a vacuum reaction chamber and by applying reaction gases to the reaction surfaces of the wafers within the reaction chamber, is proposed and preferably used.
An atomic layer epitaxy process undesirably reduces the processing speed during a process of producing semiconductor devices, thus being less likely to be used in the semiconductor device production process in the prior art. However, since the atomic layer epitaxy process can effectively accomplish a low impurity concentration and form high quality thin films on wafers, it has been actively studied to be preferably used in the semiconductor device production process. For example, a conventional thin film deposition apparatus used in such an atomic layer epitaxy process is shown in FIG. 1. As shown in the drawing, the thin film deposition apparatus comprises a gas supply unit 1 and a susceptor 3. The susceptor 3 is positioned within a vacuum chamber 4 and holds a plurality of wafers 2 thereon. The above apparatus performs a desired atomic layer epitaxy process for the wafers 2 using reaction gases supplied from the gas supply unit 1. However, the above apparatus is problematic in that it performs the desired atomic layer epitaxy process for only one wafer at a time, and so it is necessary to feed and return the wafers one by one.
This finally reduces the processing speed of the deposition process and reduces the number of wafers. For example, U.S. Pat. No. 5,338,362 of Imahashi discloses an apparatus for forming a CVD film on semiconductor wafers. This apparatus includes a cylindrical vacuum chamber, a plurality of partitioned wafer stations, and a table used as a susceptor supporting a plurality of wafers thereon. This apparatus also includes a vacuum pump and a motorized shaft for rotating the table, a lifter vertically moving the table in opposite directions, a gas supply system provided with a gas supply inlet for feeding reaction gases into the vacuum chamber, and a wafer heater for heating the wafers.
U.S. Pat. No. 5,218,274 of Yoder discloses an apparatus and method of growing thin films of the elemental semiconductors (group IVB) using modified atomic layer epitaxial (ALE) growth techniques. This apparatus includes a vacuum chamber, a plurality of server chambers seating wafers therein, a susceptor seating the wafer thereon, a vacuum pump assembly, a motorized shaft rotating the susceptor, a reaction gas supply pipe, a tail pipe connected to the reaction gas supply pipe, a plurality of gas inlets formed on the tail pipe and ejecting reaction gases into the vacuum chamber, and a wafer heater for heating the wafers.
U.S. Pat No. 6,111,225 of Ohkase discloses a thermal processing apparatus for a semi-conductor wafer. This apparatus includes a processing chamber, an upper gas supply pipe, a wafer holder, a claw support assembly mounted to the wafer holder, a support shaft connected to the wafer holder, a motor used for rotating the wafer holder, a heater used for heating a substrate, an inert gas supply pipe used for directing reaction gases to the heater. The apparatus also has a peripheral heater ring.
However, the above-mentioned three conventional apparatuses are problematic as follows. That is, the three conventional apparatuses are designed to only seat the wafers on the stations of a table within a processing chamber, supply reaction gases to the wafers within the chamber, and/or heat the wafers. Therefore, it is almost impossible for the apparatuses to achieve desired temperature conditions required to allow a desired deposition of reaction gases on the wafers, form uniform thin films on the wafers, or perform a quick process while controlling the thickness of the thin films deposited on the wafers.